Fabrics woven with warps and wefts have conventionally been used widely as an industrial fabric. They are used in various fields including papermaking wires, conveyor belts and filter cloths and required to have fabric properties suited for the intended use or using environment. Of such fabrics, a papermaking wire used in a papermaking step for removing water from raw materials by making use of the meshes of a fabric must satisfy severe requirements. There is therefore a demand for the development of fabrics which do not transfer a wire mark of the fabric to paper and therefore have an excellent surface property, have a dehydration property for sufficiently removing unnecessary water contained in the raw materials, have enough abrasion resistance and rigidity to permit desirable use even under severe environments, and are capable of maintaining conditions necessary for making good-quality paper for a long period of time. In addition, fiber supporting property, improvement in a papermaking yield, dimensional stability and running stability are required. In recent years, owing to the speed-up of a papermaking machine, requirements for papermaking wires become severe further.
Since most of the requirements for industrial fabrics and how to satisfy them can be understood by describing a papermaking fabric on which the most strict requirement is imposed among industrial fabrics, the present invention will hereinafter be described using the papermaking fabric as a representative example.
For papermaking fabrics, excellent surface property not permitting transfer of wire marks of the fabric to paper, dehydration property for sufficiently removing unnecessary water contained in the raw materials, fiber supporting property for supporting fine fibers, and rigidity permitting long-period running even under severe running conditions are very important. Research on the design or constitution of a fabric capable of satisfying the above-described properties is proceeding. Recently, two-layer fabrics using, as a portion of upper surface side warps or lower surface side warps which are vertically arranged pairs, a warp binding yarn have been employed. The warp binding yarn is woven with both an upper surface side weft and a lower surface side weft and has a binding function. At the same time, it has a function similar to that of upper surface side warp or lower surface side warp constituting a portion of the upper side surface or lower side surface.
A two-layer fabric using a warp binding yarn is disclosed in Japanese Patent Laid-Open No. 2003-342889. This fabric has excellent surface property, because it uses a warp binding yarn and therefore does not use an additional binding yarn which destroys the upper surface side fabric design. In addition, it is superior in binding strength to a weft-bound fabric. In the fabric disclosed in this document, however, two warp binding yarns forming a pair pull an upper surface side weft to the lower side at a position where they pass over an upper surface side weft, resulting in the formation of a depressed portion on the upper side surface. A height difference therefore occurs between a knuckle formed by passing of an upper surface side warp, which is not involved in binding, over an upper surface side weft and a knuckle formed by passing of a warp binding yarn over an upper surface side weft and this sometimes remains as a mark on paper. In addition, warp binding yarns forming a pair adjacently cross each other in the fabric layer so that they may block an internal space in the layer and partially cause insufficient dehydration.
Thus, fabrics using a warp binding yarn and capable of satisfying all the properties that an industrial fabric is required to have such as dehydration property, surface property and rigidity have not yet been developed.